Diazo thioethers



Patented Jan. 30, 1951 UNITED STATES PATENT OFFICE DIAZO THIOETHERS NoDrawing. Original application January 17,

1946, Serial'No. 641,866. Divided and this application February 16,1948, Serial No. 8,736

12 Claims.

This invention relates to new compounds useful as initiators (catalysts)and modifiers for the polymerization of unsaturated organic compoundseither alone or in admixture with one another, and particularly in anaqueous dispersion, which compounds form an important part of thepresent invention. This application is a division of co-pendingapplication Serial No. 641,866, filed January 17, 1946, now Patent2,501,692, issued March 28, 1950.

Unsaturated organic compounds capable of undergoing an additionpolymerization to form high molecular weight polymers may beadvantageously polymerized in the presence of the novel compounds of thepresent invention either in a homogeneous system or in the form of anaqueous emulsion. Such unsaturated organic compounds are generally thosewhich contain a methylene group attached by an olefinic double bond to acarbon atom in the structure CH2=C Compounds which contain the CH2=Cgroup and are suitable as monomers for use in the process of ourinvention include the following: butadiene-1,3; its homologues andanalogues which polymerize in the same manner, e. g., isoprene,piperylene, chloroprene, etc.; styrene; acrylonitrile; methyl acrylate;methyl methacrylate; vinyl chloride; etc. These unsaturated organiccompounds are given by way of example only. The unsaturated organiccompounds may conjugated diene hydrocarbon and a monomer copolymerizabletherewith in an aqueous emulsion. The aliphatic conjugated dienehydrocarbons (or butadiene hydrocarbons) include butadiene-1,3,isoprene, dimethyl butadiene, piperylene, chloroprene, and the like.Monomers copolymerizable with the aliphatic conjugated dienes in aqueousemulsion systems include aryl olefins and substituted aryl olefins (e;g., styrene,

p-chloro styrene, p-methoxy styrene, vinyl naphthalene, and the like),alkyl esters of acrylic acids (e. g., methyl acrylate, methylmethacrylate, butyl acrylate, and the like); nitriles of acrylic acids(e. g., acrylonitrile, methacrylonitrile, and the like), vinylidinechloride, vinyl ketones (e. g., methyl vinyl ketone), vinyl ethers,vinyl car'- bazole, vinyl furan, vinyl pyridine, and the like, all ofwhich contain the CH2=C group.

An object of this invention is to provide novel compounds, which can beused as initiators, or catalysts, in a process for the additionpolymerization of unsaturated organic compounds to form high molecularweight polymers. Another object of this invention is to provide improvedinitiators or catalysts for use in polymerization reactions of thistype. A further object of this invention is to provide compoundsparticularly suited as initiators and modifiers in the emulsionpolymerization of polymerizable organic compounds.

The diazo thio-ethers of the present invention have the generalstructural formula:

where R is a member of the group consisting of the aromatic andsubstituted aromatic radicals and R is a member of the group consistingof the aromatic, substituted aromatic, cycloalkyl, substitutedcycloalkyl, aliphatic, and substituted aliphatic radicals. These diazothio-ethers may be made by the combination of a diazotized aromaticamine and an aromatic, cycloalkyl or aliphatic mercaptan, includingsubstituted derivatives.

Examples of aromatic amines which may be used in the preparation ofdiazo thio-ethers are as follows: aniline, chloroaniline, bromoaniline,toluidine, anisidine, phenetidine, 4-aminodiphenyl ether, dimethoxyaniline, nitroaniline, methyl-methoxy aniline, trimethyl aniline,dichloroaniline, xylidine, chlorotoluidine, naphthylamine, Ydianisidine, benzidine, dichlorobenzidine, sulfanilic acid, aminobenzoicacid, toluidine sulfonic acid, naphthylamine sulfonic acid, andbenzidine disulfonic acid. Examples of merc aptans that maybe used as acoupling component in the preparation of diazo thio-ethers are thefollowing: thio-phenol, thio-cresol, chloro thio-phenol, methoxythio-phenol, thio-salicylic acid, thio-phenol sulfonic acid,thio-naphthol, 2-mercapto-3-naphthoic acid, thio-glycollic acid,

ethyl mercaptan, butyl mercaptan, t-butyl mer- 1 captan, cyclohexylmercaptan, mercapto benzothiazole, and octyl mercaptan.

The diazo thio-ethers preferred for use as polymerization catalysts inaccordance with the present invention are those in which both R- and R.in the foregoing structural formula are aromatic or substituted aromaticgroups. EX- amples of preferred compounds are substituted phenyl diazothio-(naphthyl) ethers, phenyl diazo thio-(phenyl) ethers, naphthyldiazo thio- (phenyl) ethers, and naphthyl diazo thio=(naphthyl) ethers.Preferred substituent groups are the alkyl, alkoxy, aryloxy (e. g.,phenoxy), carboxy, sulfo (SOIiH), halo, and nitro' groups; Othersubstituents give diazo thio-ethers of vary-'- ing degrees ofusefulness.

The diazo thio-ethers can conveniently be prepared by diazotizing anaromatic amine and coupling the diazonium compound with an aliphatic oran aromatic mercaptan. Diazo thio-ethers containing two diazo thio-ethergroupings. can be prepared by tetrazotizing an aromatic dia mine andcoupling the tetrazonium compound with two molecular equivalents of amercaptan. The coupling to the mercaptan is usually carried out in astrongly alkaline medium although in some examples it is advantageous tocarry out the coupling in weakly acidic media. The crude diazothio-ethers isolated from the coupling are usually of sufficient purityfor use in polymerization reactions. However, if a purified product isdesired the oil-soluble types may be purified by dissolving in acetoneor anhydrous ether at about (3., cooling to about -50 C. and filteringoff the recrystallized product. The water soluble type diazothio-ethers, in the form of their ammonium or alkali metal salts(resulting from coupling in an alkaline medium), can be convenientlypurified by washing with anhydrous ether.

New compounds prepared in accordance with this invention which arepreferred catalysts for the polymerization process of this inventionarethose represented by the formula where Ar is an aryl group and X is asubstituent selected from the group consisting of alkyl, alkoxy, aryland aryloxy radicals, n is an integer from one to four, n being at leasttwo when a methyl radical is a substituent; and R. is a member of thegroup consisting of aromatic, sub-- stituted aromatic, cycloalkyl,substituted cyclo alkyl, aliphatic, and substituted aliphatic radi cals.When a methyl substituent is employed in the aryl group attached to thenitrogen at least one other methyl (or other alkyl), alkoxy, aryl. oraryloxy radical is also present. Specific examples of new compoundsforming a part of our invention are the following: p-methoxy phenyldiazo thio-(Z-naphthyl) ether, dimethyl phenyl diazo thio-(2-naphthyl)ether, dimethyl phenyl diazo thio-(p-methoxy phenyl) ether, p-methoxyphenyl diazo thio-(o-carboxy phenyl) ether, p-

sulfo phenyl diazo thio-(2--naphthyl) ether, p-

sulfo phenyl diazo thio-(p-tolyl) ether, 2-naphthyl diazo thio-(carboxyphenyl) ether, and the like, together with the ammonium and alkali metalsalts of such compounds. Some of the more important new compounds may beconveniently represented by the formula where X is a substituentselected from the group consisting of alkoxy and aryloxy radicals, n isan integer from one to four, and R is a member of the group consistingof aromatic, substituted aromatic, cycloalkyl, substituted cycloalkyl,aliphatic, and substituted aliphatic radicals.

Conventional practice in emulsion polymerizations has been to addtogether a monomer or mixture of monomers capable of being polymerized,one or more of various initiatorsy'catalysts, and modifiers, water andan emulsifying agent. The initiator used generally is either an organicperoxide or an inorganic peroxidic material, usually used incombinationwith a modifying agent such as a mercaptan. In one commonly used systema water-soluble oxidant such as potassium persulfate is used inconjunction with an oil-soluble mercaptan which according to theory isoxidized, possibly in the aqueous or soap phase to a mercaptanfree-radical, which initiates polymer chain growth by combining with amonomer unit. There are certain inherent defects in such a chaininitiation system; and furthermore, the use of an oxidant such aspotassium persulfate may have certain undesirable features inasmuch asthe oxidant is likely to enter into certain undesirable side reactions.

We' have now discovered that the defects of the above described system,which nevertheless is the best system previously known, can be large- 13overcome through the use of diazo thio-ethers as polymerizationinitiators. Furthermore the diazo thio-ethers have the great advantageof functioning also as modifiers of chain growth, thus making itpossible to control the molecular weight and properties of the polymerwithout the use of additional modifiers. However, it is sometimesadvantageous to use supplementary modifiers in addition to the diazothio-ether.

Although the exact mechanism of chain initiation by diazo thio-ethers isnot known-it is possible that the chains are initiated by free radicalsformed by decomposition of the diazo thio-ether. Free radicals can beformed, for example, according to the following reaction:

Either or both of the above free radicals might then initiate polymerchain growth by reacting with a monomer unit according to reactions suchas the following:

RCH=CI-I2+R'S- R-CHCH2SR RLCH =CH2+R- RH+R-CH=CH The mechanism of thechain-transfer function of the diazo thio-ethers is likewise not clearlyunderstood. The chain-transfer may be brought about by mercaptansgenerated by decomposition of the diazo thio-ether. However, it may alsobe that the diazo thio-ether, itself, is a chaintransfer agent accordingto either or both of the following reactions where R represents agrowing polymer molecule:

units thus initiating new polymer chains.

The theory set forth above is a possible explanation of the mechanisminvolved in the function of diazo thio-ethers of our invention inemulsion polymerization reactions. This theory is included herein onlyas an aid in understanding the present invention and is not to beconstrued as in any way limiting the invention. Regardless of themechanism postulated, the fact remains that the diazo thio-etherseffectively catalyze and modify emulsion polymerization reactions.

One of the greatest advantages of the use of diazo thio-ethers inpolymerization reactions in accordance with our invention is their greatversatility. V Diazo thio-ethers of almost any desired reactivitycanbapreparedby suitably varying the radicals R and R. For example, if Rand R are both aromatic radicals, diazo thio-ethers of great activitycan be obtained if either or both to prepare water soluble diazothio-ethers it is only necessary that either or both of the radicals Ror R contain a water solubilizing substituent, for example, thecarboxylic or sulfonic acid groups or other hydrophilic groups. solublediazo thio-ethers are conveniently prepared and used in the form oftheir ammonium or alkali metal salts. In general the initiator activityof the water soluble diazo thio-ethers may be said to be somewhatgreater than that of comparable oil soluble diazo thio-ethers. However,both types appear to be of similar efiiciency as polymerizationmodifiers.

The type and amount of diazo thio-ether used in a particularpolymerization recipe depends upon the result desired. Forpolymerizations to be carried out at low temperatures (e. g., -10 to 40C.) an active diazo thio-ether is chosen. The water soluble types areparticularly satisfactory for low-temperature recipes. In carrying outpolymerization in an aqueous emulsion at a temperature below thefreezing point of the aqueous phase, an inert freezing point depressantis employed. For polymerizations to be carried out at highertemperatures (e. g.-, 40-60 C.)

diazo thio-ethers of moderate activity are chosen while for even highertemperature polymerizations diazo thio-ethers of low activity areselected. In general, approximately 0.2 part by weight of the diazothio-ether, based on the weight of the monomeric material, will givesatisfactory promotion although other proportions within the range ofabout 0.05 to about 5.0 parts by weight, based on the weight of themonomeric a dodecyl mercaptan to the polymerization recipe.

Typical examples of our invention are the following:

Earample I 123 parts of p-anisidine are dissolved in 3,000 parts ofwater with 91 parts of hydrogen chloride (100%) used as 36% solution.The resulting solution is cooled to to C. and diazotized by the additionof 70 parts of sodium nitrite dissolved in 200 parts of water. Thediazonium solution is poured rapidly into a solution of 163 parts ofthio-beta-naphthol andj400 parts of sodium hydroxide in 4,500 parts ofwater at Such water 0.150 5 C. The diazo thio-ether, p-methoxy phenyldiazo thio-(2-naphthyl) ether, immediately precipitates as a finelydispersed oil, which soon solidifies to a yellow solid. The solidmaterial is filtered off, washed thoroughly, and

dried at room temperature under vacuum. This thio-ether is oil soluble.

Two parts of the diazo thio-ether are added to an agitated autoclavecontaining water 180 parts, soap 5 parts, butadiene '75 parts, andstyrene 25 parts. Agitation is continued for nine hours while the chargetemperature is maintained at 50 C. by means of water circulation in theautoclave jacket. At the end of nine hours the charge is discharged intoa stripping tank where the unreacted monomers are recovered bysteamdistillation. The latex is creamed by the addition of a small amount ofsodium chloride solution and coagulated by the addition of dilutesulfuric acid. The rubber crumb is washed several times by decantationand, finally, dried in a vacuum oven at 60 C. The product, which is thusobtained in about conversion based upon the weight of starting monomers,is a soft, well-modified rubber which is soluble in benzene and has goodproperties when compounded and vulcanized in conventional ways.

Example II parts of beta-naphthylamine are diazotized in 2,000 parts ofwater containing 250 parts of 10 N hydrochloric acid by the addition ofa solution of '70 partsof sodium nitrite. The resulting diazoniumsolution is run slowly into a solution of 162 parts of thio-salicylicacid in 10,000 parts of" water containing 80 parts of sodium hydroxideand 410 parts of sodium carbonate. The sodium salt of beta-naphthyldiazo thio-salicylic acid precipitates and is filtered and washedthorough- 1y with 10% sodium sulfate solution and, finally, once with asmall amount of cold water. The product, 2-naphthy1 diazo thio-(carboxyphenyl) ether, is dried at room temperature under vacuum. If desired itcan be purified by washing with a little anhydrous ethyl ether. Theresulting product is of the water soluble type.

When used in a polymerization recipe-essentially as described in ExampleI, the results are comparable to those of Example I.

Example III 1'73 parts of sulfanilic acid are .diazotized in 2,000 partsof water containing 25 parts of 10 N hydrochloric acid by the additionof a solution of 70 parts of sodium nitrite. The cold diazonium solutionis poured rapidly into a cold solution of 131 parts of p-thio-cresol in5,000 parts of water containing 80 parts of sodium hydroxid and 82 partsof sodium acetate. The bright, yellow sodium salt of the diazothio-ether precipitates immediatel and is isolated, washed, and dried asin Example II. Thi product, p-sulfo phenyl diazo thio-(p-tolyl) ether,is of the water soluble type.

One part of the diazo thio-ether is added to-a polymerization mixturecontaining parts of water, 5 parts of Aerosol AY (a commercial,synthetic detergent described as a succinic ester sulfonate), '75 partsof butadiene, and 25 parts of styrene. Polymerization is carried out at50 C. for 12 hours and the rubber isolated by methods analogous to thoseof Example I.

Example IV amogom 7 ie sale, p-me'tho'xy lzphenyl fdiazo thio-(e'arboxy)"DhenyD ether, "(a *diazo thiotherpf the water soluble type), are addedto a polymerization recipe containing 180 Iparts of water, .5 parts ofAerosol AY, 75 parts of butadiene, and 25 .parts o'f styr'ehe.Polymerization is carriedout at 25 C. for twelve hours and the productisolated as in Example I. A wen 'mo'difie'd rubber of .good propertiesis obtained.

Example V 053 part "of the diazothio-ether of Example 51 is added to apolymerization recipe containing 180 parts of water, 5 parts of soap, 04part of dodecyl mercaptan, '75 arts of butadiene and 25 parts ofstyrene. Polym'eriz'ation i continued for 12 hours at 50 C. and theproduct isolated as in Example -I. Aw'ell modified :ru'bber 01 goodproperties is'obtained.

Example V1 '03 part of "the diazo'thio-ether'of Example Iis added to apolymerization recipe containing 180 parts of water, 5 parts of soap,0.2 partof potassium persulfa tejwl part of tertiar dodecyl mercaptan,'75 parts o'f'butadieneand 25 parts of styrene. Polymerization iscontinued for hours and the rubber isolated as in Example I.

Example -VII An'aut'oclaveiis charged exactlyas in Example I except thatis'oprene is used in place of the butadi'ene. A comparable rubber "ofvery good properties isobtain'ed.

Example VIII Two parts of the diazo'thio-ether'of Example I are added toa polymerization mixture of water 180 parts, soap 5 .parts, butadiene 75parts and methyl methacrylate parts. Polymerization proceeds rapidly at50 C. to give an elast'or'ner having certain very desirable'properties.

Example IX One part of the di'azo thio-ethero'f Example l i added to'100 parts of ethyl acrylate. The -so lution 'is run slowl into anagitated autoclave containing 150 parts of water and one part of AerosolAY, thebatch temperature being maintained at 50 C. 'An acrylic polymerof valuable properties is obtained.

Example X One part of the oil soluble diazo thio-"ether,.pchloro phenyldiazo thiO-(Z-naphthyl) ether, prepared by coupling diazotizedp-chloroaniline with thio-beta-naphthoLis dissolved in 100 parts ofmethyl methacrylate and polymerized .ia's in Example IX. -A methacrylate'poylm'er -of valuable properties is obtained.

Example XI Two parts of the diazo thio-ether of Example I are added "toa polymerization recipe of "180 parts of water, 5 partsof soapjfloparts'of'butadiene and parts of'acrylonitrile. Polymerization is-carried 'outat5'0' 'C. andthe product isolated 'asin Example" I.

Example Jill A polymerizatio'nis carried out exactly as in Example Iexcept that vinyl pyridine is used in .place of styrene. Awell modifiedrubber ofsgood -Pt opertiesis-obtained.

Example XIII A polymerization is carried out exactly as in Example Iexcept that dichlorostyrene is used in -place of styrene. A wellmodified rubber of gOOd prope'rties is obtained.

Example XI-V Two parts of the diazo thio-ether prepared in Example I areadded to a polymerization mixture consisting of 180 parts of Water, 5parts of dodecyl ammonium acetate, parts of butadiene and 25 parts ofstyrene. Polymerization is carried out at 40 C. The stripped latex iscoagulated, isolated and driedin the usual way.

Example XV 05 part of the diazo thio-ether, dimethyl phenyl diazo thio(2.-naphthyl) ether, prepared bycoupling 'diazotized m-xylidine withthio-betanaphthol is added to a polymerization mixture containing partsof water, '5 parts of soap, '75 parts of butadiene and 25 parts ofstyrene. Polymeriza'tion is carried-out at 50 C. for 3 hours to obtain a65% conversion ofa soft, well-modified rubber of good properties. Whenthe diazo thioether was replaced'by 0.3 part of potassium persulfateand0.5 part of dodecyl mercaptan in the abov recip'e, ten hours wererequired to effect the same amount of conversion.

Example XVI The polymerization of Example I was carried outin which atotal of 0.75 part'of the diazo thioether was added in increments as thepolymerization proceeded. 0505 part of the promoter was added at thebeginning of the reaction, 0.3 part was added at the end of one hour and0.4 part was added at the end of four hours. Polymerization "conversionwas 75% "in seven hours at 50 .C. The'rubber was completely soluble inbenzeneiand had 'very good properties. This increiment'manner ofaddition was found to decrease materially theproportion of diazothio-ether'required' while providing uniform modifying action. I heforegoing examples illustrate preferred methods of practicingthis-invention and are to be construed as being illustrative only,without inany'way limiting the scope of the invention.

-An impor-tant advantage of the process of this invention-and thecatalysts employed therewith is illustrated in the examples illustratingthe use of dia'zo thio-ethers of both the oil-soluble and thewater-soluble types. "The choice o'f the diazo thio-ether also effectsthe rate of polymerization as is illustrated in the examples. Catalystsof our invention may be employed to efiectvery rapid polymerization ofthe monomeric materials, if desired, and make possible continuousemulsion polymerization in lieu of th conventional batch process.

present invention are found to have excellent z'proper-ties when"evaluated .in icomp'arison with standardsynthetic'rubbers inconventional compounding-recipes. Standard tread stocks'prepared fromlpolymers made in accordance with the pres- 'ent invention have roomtemperature tensile trengths in the range Tof 3000 to 35001poun'cls:per

square inch or more and room temperature elongations in the range of 600to 800 per cent or more. Other properties such as hysteresis, flex life,abrasion resistance, etc., of the products of the present invention inmany cases possess definite superiority over polymers produced byconventional methods.

Although we have disclosed specific embodiments of our invention, itwill be apparent that the initiators and polymerization process of ourinvention are capable of broad application in the art, and that variousmodification may be made without departing from the scope of theinvention.

We claim: V

1. Diazo thio-ethers represented by the formula R-N=N-SR' where R is ofthe group consisting of naphthyl, dimethylphenyl, methoxyphenyl,chlorophenyl, and sulfophenyl, and R is of the group consisting ofnaphthyl, methylphenyl, methoxyphenyl, and carboxyphenyl.

2. Sulfo phenyl diazo thio-tolyl ether.

3. p-Sulfo phenyl diazo thio-(p-tolyl) ether.

4. Chloro phenyl diazo thio-naphthyl ether.

5. p-Chloro phenyl diazo thio-(2-naphthyl) ether.

6. Methoxy phenyl ether.

7. p-Methoxy phenyl diazo thio-(naphthyl) ether.

diazo thio-(naphthyl) diazo thio- (naphthyl) 12. p-Methoxy phenyl diazothio-(carboxy phenyl) WILLIAM B. REYNOLDS. RICHARD K. HARRIS,Administrator of the Estate of Ernest W. Gotten,

Deceased.

REFERENCES CITED The following. references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,251,156 Nygaard .a July 29,1941 2,376,963 Garvey May 29, 1945 OTHER REFERENCES Chem. Abst., v01.22,page 4465 (1928), citing Finzi-Gazzetta Chimica Italiana, vol. 58,pp. 269- 278 (1928).

Berichte Deut. Chem., Vol. 28. pages 3237 to 3251 (1895).

1. DIAZO THIO-ESTHERS REPRESENTED BY THE FORMULA R-N=N-S-R'' WHERE R ISOF THE GROUP CONSISTING OF NAPHTHYL, DIMETHYLPHENYL, METHOXYPHENYL,CHLOROPHENYL, AND SULFOPHENYL, AND R'' IS OF THE GROUP CONSISTING OFNAPHTHYL, METHYLPHENYL, METHOXYPHENYL, AND CARBOXYPHENYL.